Semiconductor device production processes include the step of locally implanting an impurity (ions) such as phosphorus, arsenic or boron, for example, into a front surface (major surface) of a semiconductor wafer (hereinafter referred to simply as “wafer”). In order to prevent the ion implantation into an unnecessary portion of the wafer, a resist pattern of a photosensitive resin is formed on the front surface of the wafer to mask the unnecessary portion of the wafer with the resist in this step. After the ion implantation, the resist pattern formed on the front surface of the wafer becomes unnecessary. Therefore, a resist removing process is performed for removing the unnecessary resist from the front surface of the wafer after the ion implantation.
In a typical resist removing process, the front surface of the wafer is irradiated with oxygen plasma to ash the resist on the front surface of the wafer. Then, a chemical liquid such as a sulfuric acid/hydrogen peroxide mixture (SPM liquid) which is a liquid mixture of sulfuric acid and a hydrogen peroxide solution is supplied to the front surface of the wafer, whereby the ashed resist is removed. Thus, the removal of the resist from the front surface of the wafer is achieved.
However, the irradiation with the oxygen plasma for the ashing of the resist damages a portion of the front surface of the wafer uncovered with the resist (e.g., an oxide film exposed from the resist).
Therefore, a resist removing method such that the SPM liquid is supplied onto the front surface of the wafer to lift off the resist from the front surface of the wafer by the strong oxidative power of peroxosulfuric acid (H2SO5) contained in the SPM liquid without ashing the resist has recently been attracting attention.